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Precipitation of  Sodium Diuranate from Alkaline Lean Liquor

S.Siddique1*, K.Srinivas1 and N.R.Mandre2

1Uranium Corporation of India Limited,Tummalapalle, YSR Kadapa District,516349 Andhra Pradesh, India.
2Department of Fuel and Mineral Engineering, Indian School of Mines University, Dhanbad, 826004  Jharkhand, India.

ABSTRACT:

No two deposits being identical, the extraction of metal from any given ore requires specifically tailored process route and equipment. The process information required for any given situation often has to be generated experimentally, which requires laboratory work and can also entail extended and extensive pilot plant test. These test results help in designing and operation of the full scale plant.

KEYWORDS: Sodium Diuranate;Lean Liquor

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Siddique S, Srinivas K, Mandre N. R. Precipitation of Sodium Diuranate from Alkaline Lean Liquor. Mat.Sci.Res.India;10(2)


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Siddique S, Srinivas K, Mandre N. R. Precipitation of Sodium Diuranate from Alkaline Lean Liquor. Mat.Sci.Res.India;10(2). Available from: http://www.materialsciencejournal.org/?p=152


INTRODUCTION.

There are two primary sources from which human being derives material wealth. One is things that grow and are harvested, which gives us agriculture, fishing, forestry etc. The other is materials in the ground that we discover and exploit by mining, beneficiation, metallurgical processing and manufacturing. Geologists discover ores, miners extract them from the earth and metallurgists process them to extract the metal.

No two deposits being identical, the extraction of metal from any given ore requires specifically tailored process equipment. The process information required for any given situation often has to be generated experimentally, which requires laboratory work and can also entail extended and extensive piloting 1.

A good understanding of the nature of mineralization of uranium values in the ore, uranium process chemistry and different unit operations, has led to the development of well integrated specially engineered alkaline process flow sheet to treat the low grade uranium deposit in the alkaline host rock 2.

PROCESS DESCRIPTION

PROCESS DESCRIPTION
Click on image to enlarge

 

The Pure Hot Clarified liquor from the Clarification area is the input for Uranium precipitation.

Sodium Diuranate (SDU) slurry shall be precipitated from pregnant mother liquor by controlled addition of Sodium hydroxide to raise the pH to 12.0 which is the optimum pH for the precipitation reaction. Twelve mechanically agitated reactor tanks are provided in series for the precipitation of SDU 3.

The Pure Hot Clarified liquor will be stored in the Pure Hot Clarified Liquor Tank. Two Clarified Hot Liquor Pumps, one working one standby) have been provided to pump the liquor to the first of the twelve Sodium Diuranate Precipitation Tanks. Sodium hydroxide at 45% solution strength will be dosed in the first two Sodium Diuranate Precipitation Tanks. Two reactions takes place in the precipitation tanks. First, sodium hydroxide reacts with the excess NaHCO3 to give Na2CO3

NaHCO3 + NaOH    →    Na2CO3 + H2O

NaOH also reacts with sodium uranyl carbonate to precipitate sodium diuranate.

2 Na4UO2(CO3)3 + 6NaOH    →    Na2U2O7 + 6Na2CO3 +H2O

Provision of recycling a part of the SDU thickener under flow to the first precipitation tank has been provided for seeding purpose after carbonation. Attached figure clearly reveals the impact of liquor concentration on precipitation of SDU 4.

The over flow from each tank shall gravitate to the next tank in series. The third, 7th and the 12th tanks will have pH sensors to monitor the pH of the slurry and will control the sodium hydroxide addition in the first two tanks. The over flow from the last tank will gravitate to the SDU Thickener

Provisions for flocculant addition in the SDU Thickener has been envisaged.  This will help not only in maximizing the underflow consistency but also ensure clear overflow from the thickener. The addition rate of the flocculant solution will be established depending upon the overflow clarity. The bed mass pressure transmitter located at the thickener bottom ensures underflow withdrawal at peak consistency. Thickener overflow is collected in SDU Thickener overflow tank. Which is then pumped to SDU Filtrate Tanks by SDU Thickener overflow pumps

The thickened underflow from the SDU thickener is pumped with the help of SDU underflow pumps to the Product Settling tanks which are provided with Product Settling Tank Agitators. The liquor in the underflow will have some associated dissolved solids. This dissolved solid concentration will be reduced to a minimum by dilution washing in the Product holding Tank. Flocculant is dosed in the tank to increase the settle ability of the washed solids. The supernatant generated is siphoned off and sent to Product settling overflow sump. The settled mass is pumped to Horizontal Belt Filter. These pumps are provided with VFDP to control the feed rate to the filter.

The Horizontal Belt filter for dewatering the product will have a filtration area of 5 Sq.M.  Provision for washing the cake with industrial water has been made.  The length of the belt will ensure a dry cake on a consistent basis.

Two Vacuum Pumps each with a displacement capacity of 500   M3/Hr will be provided. The suction end of the pumps will be connected to a header for easy interchangeability of the pumps.

The Horizontal belt filter operates for 12 hours. The cake discharged from the Belt filter needs to be reslurried to a precise consistency to make it amenable for the next processing step. To ensure this, the cake from the filter is first taken to the SDU Cake Primary Repulper which is provided with agitator. Industrial water will be added to the tank to repulp the cake to make the slurry consistency to 30%. From the Primary Repulper the slurry will be stored in the SDU Slurry Tank. The SDU Slurry Tanks are provided with SDU Slurry Tanks Agitators  to keep the slurry in suspension. Two Sodium Diuranate slurry pump are provided to pump the SDU slurry from the SDU Slurry Tanks to the Spray Drying section. Density meter on the discharge line of the Sodium Diuranate slurry pump will monitor the density of the pulp being taken for drying.

The Product settling tank over flow as well as the cloth wash water is likely to contain some amount of the valuable product and needs to be recovered. A separate SDU Spillage Thickener has been provided for this purpose. The flow to the thickener will comprise of cloth wash water from the belt filter, spillage from Chemical House Floor Wash Sump and flow from Product Spillage Sump.  The Level indicator controller placed in the Thickener will be interfaced with the VVVF of the Flocculant dosing pumps to dose flocculant in the thickener at a controlled rate based on the level in the Thickener. The underflow withdrawal by Thickener Underflow Pumps will be managed through bed mass measurement which will control the withdrawal by controlling the pump speed through the VVVF and this underflow is sent back to the Product thickener. Spillage Thickener overflow will be collected in Spillage Thickener overflow tank and will be pumped by the Spillage Thickener overflow pumps to chemical house for floor wash.

X-AxisU3O8 in Clarified Pregnant Liquor(gpl). 0.455 0.518 0.579 0.614 0.739 0.866 0.942 1.500
Y-Axix% Precipitation. 50.26 58.68 69.43 82.57 83.76 84.64 89.59 95.00

Table: Effect of liquor concentration on recovery of SDU

 

Figure: Effect of liquor concentration on recovery of SDU
Click on image to enlarge

CONCLUSION.

Raising the concentration of uranium in leach liquor to a level which is suitable for direct precipitation of uranium as Sodium di-uranate is a big challenge. How ever, in case of failure to get desired concentration of uranium in leach liquor, precipitation of uranium as Sodium di-uranate could be effected by adding dissolved Sodium di-uranate solution in the first tank of the precipitation circuit.  Dissolution of Sodium di-uranate can be effected by partial withdrawal of SDU thickener underflow.

ACKNOWLEDGMENT.

I would like to acknowledge the whole hearted support that I have received  from my colleagues , vendors and the consultants who have given their best to accomplish the task in really a short time frame.  I would also like to acknowledge the support rendered by Chairman and Managing Director, UCIL and  Director (Technical), UCIL.

REFERENCES.

  1. Using Computing Power in Process Development by Mike Dry, Arithmetek Inc.
  2. Innovative Process Flow sheet for the recovery of Uranium from Tummalapalle Ore by Dr A K Suri, Director, Materials group, BARC, Mumbai.
  3. Basic Engineering Package (BEP) by M/s Hindustan Dorr Oliver Ltd, Mumbai.
  4. IAEA Interregional Training Course on Uranium Exploration Strategy, Mining and Processing Technology.
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